Cobalt sulfur containing

C.-H. Kiang e o/.[33] reported that the singlelayered coiled lubes were obtained by co-vaporizing cobalt with carbon in an arc fullerene generator. A single-layered helical structure with radii of curvature as small as 20 nm was seen. These helically coiled forms lend to bundle together. In the soot obtained with sulfur-containing anodes, they also found the 1.3-nm diameter lube coil around the 3.6 nm tube (see Fig. 14). This kind of structure was theoretically proposed in ref. [14]. 

Catalysts used for hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of heavy oil fractions are largely based on alumina-supported molybdenum or tungsten to which cobalt or nickel is added as a promoter [11]. As the catalysts are active in the sulfided state, activation is carried out by treating the oxidic catalyst precursor in a mixture of H2S and H2 (or by exposing the catalyst to the sulfur-containing feed). The function of hydrogen is to prevent the decomposition of the relatively unstable H2S to elemental sulfur, which would otherwise accumulate on the surface of the... 

The methods described here are based on the thermal stability of such clusters under CO pressure.4 In the case of Co2Fe(CO)9S, the complex itself is stable under hydroformylation conditions (130-180 °C, 50-150 bar CO and H2) and is formed under such conditions from almost every sulfur-containing substance, iron, cobalt, and carbon monoxide.1 Ethanethiol is used in the procedure as the sulfur source because of its reactivity. The dihydride cluster Fe3H2(CO)9S is not directly accessible by this method because it is a thermally much less stable species but the anion Fe3H(CO)9S" can be prepared in this way and its acidification yields the desired complex. 

Reduction. Benzene can be reduced to cyclohexane [110-82-7], C5H12, or cycloolefins. At room temperature and ordinary pressure, benzene, either alone or in hydrocarbon solvents, is quantitatively reduced to cyclohexane with hydrogen and nickel or cobalt (14) catalysts. Catalytic vapor-phase hydrogenation of benzene is readily accomplished at about 200°C with nickel catalysts. Nickel or platinum catalysts are deactivated by the presence of sulfur-containing impurities in the benzene and these metals should only be used with thiophene-free benzene. Catalysts less active and less sensitive to sulfur, such as molybdenum oxide or sulfide, can be used when benzene is contaminated with sulfur-containing impurities. Benzene is reduced to 1,4-cydohexadiene [628-41-1], C6HS, with alkali metals in liquid ammonia solution in the presence of alcohols (15). 

Further evidence that cobalt metal is not responsible for the catalytic hydrogen waves comes from the observation that the higher the stability of the complex formed between the sulfur-containing ligand and Co2+, the more pronounced is the catalytic wave.378 This is confirmed since... 

The thermochemical aspects of these reactions have been discussed in terms of heats of formation of the halides of elements of the iron group, and of the acceptor metal (75). The yield of carbonyls was especially favored with the iodides and also with sulfides or sulfur-containing materials (76). With iron and cobalt iodides the reaction is facilitated by formation of the carbonyl iodide as an intermediate. 

The hydrogenolysis of sulfur-containing compounds is also an important industrial process, known as hydrodesulfurization, in the field of petroleum refinery to reduce the sulfur content of petroleum fractions. The most commonly used catalyst is a mixture of either cobalt or nickel and molybdenum oxides supported on alumina, which is sulfided before use and usually employed at about 300-400°C and 1-7 MPa H2.128 The basic reactions involved in the hydrodesulfurization process are represented in eq. 13.60. 

Both sulfide and disulfide are more commonly encountered as bridging ligands in cobalt clusters. There are few systematic syntheses. For example, [Co2(CO)g] reacts at room temperature with CS2 either neat or in the presence of hydrocarbon solvents to form [Co3(S)(CO)c,], [Co6(C)(S)2(CO)12] and at least three other sulfur-containing derivatives in addition to sulfur-free species such as [Co3(CXCO)9].979 Similarly, [Co2(CO)g] with elemental sulfur in hydrocarbon solvent gives [Co3(S)(CO)9], [Co4(S)2(CO)l0], [Co6(S)3(CO)6] and [Co6(S)4(CO) 4],980 with the product distribution dependent on the reaction conditions. Details of several cluster preparations are given in Table 79 and structural data in Table 80. 

Analogous complexes of cobalt(III) containing a tetradentate ligand (L4) have furnished strictly parallel results. Accordingly, the insertion was observed to occur either in neat SO2 or in DMF solution with RCo(salen)H20 when R = Me 36, 82, 100) or Et (36, 100), but not when R = Ph or CsFg (36). The complexes MeCo(salophen)H20 (36) and MeCo(bae)H20 (82) also yield the corresponding 5-sulfinates on treatment with sulfur dioxide. 

The use of Fe-Cr and especially Cu-Zn-Al WCS catalysts in present-day hydrogen plants is directly connected with moderate levels of sulfur-containing compounds in natural gas and naphtha that almost completely displaced coal as the feedstock. It is likely, however, that the incentives for the use of fossil fuels rich in sulfur can be revitalized in the future. If this scenario comes into play, sulfur-tolerant catalysts will be a must for WCS process. Such catalysts are already developed, but so far they have only found a limited use in some particular cases where feed gases with high concentrations of CO and sulfur compounds had to be converted. The best known of this type are cobalt-molybdenum compositions, which are usually supported over alumina and may be promoted with alkali... 

---